Host computers send input/output (I/O) requests to storage arrays to perform reads, writes, and maintenance. The storage arrays typically process the requests in a fraction of a second. In some instances, numerous hosts direct large numbers of requests toward a single storage array. If the array is not able to immediately process the requests, then the requests are queued.
I/O requests received at a storage device are processed according to predefined priorities. Historically, Small Computer System Interface (SCSI) storage devices had limited information for use in prioritizing I/Os. Thus, all I/Os were processed with a same priority and quality of service (QoS).